SAN FRANCISCO — Facebook is losing young users at an even faster clip to Snapchat than previously forecast, according to new research from eMarketer.

Less than half of U.S. Internet users ages 12 to 17 will use Facebook this year for the first time, the research firm says.

And the giant social network can no longer count on Instagram to help retain that younger audience, according to eMarketer.

Facebook will lose 2 million users under 25 this year, eMarketer estimates. Not all of those users are migrating to Instagram, also owned by Facebook.

Instagram will add 1.6 million users in that age group while Snapchat will add 1.9 million users, according to eMarketer. The research firm, which bases its analysis on survey and traffic data from research firms and regulatory agencies, Facebook press releases, historical trends, Internet and mobile trends and other factors, says Snapchat will continue to have more users ages 12 to 24 than Instagram.

Facebook declined to comment.

This is just the latest in a growing body of research that suggests young people are logging in less frequently and spending less time on Facebook. What's more: There are now "Facebook nevers," children becoming tweens who are skipping Facebook altogether. Facebook requires members to be 13 to sign up, though many kids under that age access social media by having their parents start their account.

EMarketer analyst Debra Aho Williamson says her teenage daughter lost access to her Facebook account when she got a new phone two months ago. "Sometimes she says to me: 'My Facebook doesn't work.' But she doesn't ask me to get it going for her again."

With more than 2 billion users, Facebook is still the world’s most popular online hangout. But for years now, the social network’s growth in the U.S. has been driven by older users. The number of total users in the U.S. this year will grow by just less than 1% to 169.5 million, according to eMarketer. And eMarketer expects Facebook’s proportion of social network users in the U.S. to continue to decline through 2021.

This is the second time in less than six months that eMarketer has warned about the fading appeal of Facebook for teens. It's a grown-up problem for Facebook, which needs young users to develop the habit of checking Facebook so it can show them advertising into adulthood. Late last year, Facebook launched a kids version of its Messenger app targeted at 6- to 12-year-olds, igniting debate over whether children that young should be using social media.

Julie Smith, a social scientist in Denver who works with teens, says they call Facebook “the old people network.”(Photo: Adam Beach, Adam Beach Photography)

Julie Smith, a social scientist in Denver who works with teens, says they call Facebook “the old people network.”

“Teens want that instant gratification. That’s why Snapchat and Instagram work well for them. Their minds move quickly,” Smith says. “Facebook feels like an investment of their time, and they don’t want to invest their time in it.”

Smith’s 17-year-old son Finnegan, who spends the bulk of his social media time on Snapchat and occasionally Instagram, recently deleted the Facebook account that he rarely used. Facebook, he says, "was too much to keep track of."

The ephemeral nature of Snapchat is a big draw for teens. So, too, is the ability to communicate one on one or in smaller groups. Teens have had warnings drilled into them that one wrong move on Facebook could hurt their chances of getting into college or landing a job so they like the ability to be more selective about what they share and with whom, Finnegan Smith says.

“Snapchat is what a lot of people use just because it’s really easy to connect with people one on one and you can choose to share with a lot of people or you can choose to have it be more private,” he said. “I don’t think Facebook panders to teenagers as well as it does to older generations. I think that’s definitely something they need to work on.”

Facebook use among those younger than 12 will decline 9.3% in 2018, eMarketer predicts. Growth among 12-to-17-year-olds and 18-to-24-year-olds will decrease by more than 5%.

This is the first time eMarketer has predicted a decline in Facebook usage among 18- to 24-year-olds and those younger than 12.

Instagram is still bigger overall in the U.S. than Snapchat. The number of Instagram users will total 104.7 million users, up 13.1% year over year. Snapchat is expected to increase 9.3% to 86.5 million users.

Facebook bought Instagram in 2012 for $1 billion in search of the social media fountain of youth. It admitted in 2013 that young people were hanging out on Facebook less frequently.

"Facebook knew they needed something else in their arsenal to keep the interests of teens and young people, and to a large extent, Instagram has done that," Williamson said.

When Facebook's $3 billion-plus takeover offer was rebuffed by Snap, the parent company of Snapchat, the social network began cloning the buzzy chat app's features on Facebook and Instagram.

That has not made a difference to Smith, who says he may open a Facebook account again someday. But not right now.

"I’m not sure anything could bring me back to the site at this moment in time,” he said. “With the wide variety of social media out there, it’s easy for everyone to find something that fits them well. For a lot of people, that’s something like Facebook. For a lot of people, that’s something like Twitter. For a lot of people, that’s something like Snapchat. Everyone has their social media match when it comes to these sites. For now, for me, that’s not Facebook.”